Microbiologically Induced Corrosion (MIC) [also referred to as Microbially Influenced Corrosion] is corrosion involving bacteria interacting with metal surfaces. Several bacterial species exist and cause corrosion with different combinations of materials and chemical constituents. By example, MIC is recognized in water filled and crude oil systems, attacking carbon steel and stainless steel. Generally described as pitting of the metal, MIC also produces cavern-like voids and tunnel-like voids within the metal which results in the overall reduction of metal thickness.
Chemical, electrochemical, and biological analysis of the fluid medium have been used to detect the presence of MIC in a system. Radiography has been used to detect MIC at its location in the metal. These techniques are time consuming and costly to implement or provide such limited information about the location and severity of MIC to make them ineffective for repairing the damage in metal systems caused by MIC. Faced with bacterially induced corrosion, system operators typically change the material of construction or implement elaborate programs to control the bacteria as a preventive technique.
The methodology of this invention is to thermally stimulate the fluid within the MIC produced cavity or pit, causing that fluid to flow and/or to boil. Both flowing fluid and boiling produce acoustic energy, detectable with the nondestructive test method known as acoustic emission. The acoustic energy detected during thermal stimulation leads to the detection, location, and severity of the MIC damage. This method is more cost effective than present detection techniques and permits corrective action in the form of immediate repair or planned future maintenance based on the severity of damage present.
Acoustic emission has been used to monitor piping systems and vessels (tanks) in a variety of industries. Pressurization is the dominant form of stress (stimulus) application. Heaters have also been used to test flywheels for cracks; the heating of spokes producing sufficient stress in critical regions to yield acoustic emissions if a crack had been present. Mechanical loading of components, as in a three point bending application or dead weight on a steel rod, is also a common stress technique.
Commercial equipment is available which uses a thermal (hot-tip) probe to measure conductivity and/or wall thickness and/or surface cracks, but it is based on thermal conductance away from the probe or from a heater probe to a receiver probe. The application of this method to the detection of corrosion such as MIC is not known to exist.
The present invention provides an efficient, accurate, and nondestructive method to detect the presence of MIC damage or other corrosion damage in components and systems. The invention also provides a technique to locate the position of MIC-damage in a component or system and to establish the severity of the MIC-damage, wherein severity is related to the volume of metal corroded and/or the depth to which the MIC has progressed towards the outer surface of the component.
The present invention also provides a technique to detect, locate and assess MIC severity when the system or component has been drained of its contents; but not dried to the extend of removing fluid from MIC damage sites. It may also be use on a variety of metallic materials with various geometries and various fluid contents. In addition, during use of the invention, the invention may be employed to detect damage mechanisms through acoustic sources such as cracking, boiling, fluid flow or material deformation as a result of heating or thermally straining the region in which damage exists.